Many different types of snow plows are known to the art. Conventional plows include a blade and a frame for coupling the blade to the front of a vehicle. More sophisticated plows also include means for adjusting the angular orientation of the plow blade relative to the longitudinal axis of the vehicle and for elevating the plow blade relative to the road surface to permit the vehicle to be driven from one location to another.
Prior art snow plows are also known for use with many different sizes of vehicles. For example, plows are known which can be used with very large vehicles. These plows are typically used for large snow removal jobs such as airport runway clearing and the like. Smaller plows are known which can be coupled to dump or garbage trucks for use in road clearing operations, and still smaller snow plows are know which may be coupled to yet smaller trucks for use in driveway or parking lot clearing and the like. A typical example of the latter would be the type of plow frequently employed by the owner of a gasoline station for use with his tow or pick-up truck. Following a snowfall, such a plow would be coupled to the front end of the tow truck for use in clearing the station as well as for other snow clearing jobs in the neighborhood.
The type of plow just referred to is usually quite expensive, requires considerable time to attach to a vehicle, and includes structural features which makes them impractical for use with cars. For example, such plows commonly include a hydraulic pump assembly mounted externally of the vehicle, a feature which increases the exposure of the operating components to adverse weather conditions and increases the likelihood of theft or vandalism of the equipment. Moreover, such plows also include a bulky, view-obstructing plow lifting system mounted immediately adjacent the front end of the vehicle which includes a hydraulic cylinder oriented upwardly to engage a lifting arm which in turn is coupled to the plow by a chain. Extension of the cylinder causes the arm to be elevated which in turn causes the chain to lift the plow blade above the road surface. This type of lift system, both because of its bulk and because of its tendency to shift weight off the back wheels of the vehicle, make this type of plow unsuitable for smaller vehicles such as cars. Typical examples of this type of plow are described in Simi's U.S. Pat. No. 3,037,275, issued Mar. 7, 1967, for "Vehicle Accessory Unit and Power Unit Therefore," and in Micelli's U.S. Pat. No. 3,706,144, issued Dec. 19, 1972, for "Control Means for a Snowplow." Also, the devices described in these patents make no provision for locking the blade in its elevated position. Driving a snow plow at a high rate of speed with an elevated blade is potentially dangerous, because any failure of the hydraulic system could cause the blade to fall to the road surface resulting in damage to the vehicle, or more importantly, injury to the driver. A similar result could occur if the lifting chain breaks or is accidently uncoupled from the plow.
Another related type of snow plow is described in Jackoboice's U.S. Pat. No. 3,524,269, issued Aug. 18, 1970, for "Mounting Means for Vehicular Implements." This device is different from that described above in that instead of using a vertical frame and upwardly directed hydraulic cylinder for raising the plow, it employs a horizontal cylinder which rotates a round member mounted to the plow blade frame to lift the plow. The vehicle's bumper supports one end of a lifting chain. The other end of the chain is attached to the round member and is wound therearound at the discretion of the driver to cause shortening of the chain length and resultant lifting of the blade. While the lifting mechanism is different, this type of plow still suffers from the same disadvantages as those discussed above which significantly impair the adaptability of this type of plow for use with small vehicles, such as cars.
Yet another type of lifting system for plow blades and the like is illustrated in Holopainen's U.S. Pat. No. 3,165,842, issued Jan. 19, 1965, for "Mechanism for Attaching Implements to Vehicles." In the described device a link is located intermediate the subframe assembly and the implement and a cylinder acts on the link to rotate it and push the implement upward.
None of the aforementioned systems are entirely satisfactory for use with small vehicles, such as cars. This special utility requires ease of attachment, a lift system which will not obstruct the driver's view and a blade lift system which does not cause detrimental weight distribution problems or alter the vehicle's normal driving characteristics. The development of a snow plow assembly which would obtain these objects and overcome the difficulties of the prior art would be a significant advance in this technology.